1. Field of the Invention
The present invention relates to an optical scanning device, an image forming apparatus, a mirror, a housing, a mirror attaching method, a mirror arrangement adjusting device, and a mirror arrangement adjusting method.
2. Description of the Related Art
For a color image forming apparatus such as a laser printer, a digital copying machine and a laser FAX, there are provided a polygon mirror for deflecting a scanning light beam from a light source and formed into a regular polygon shape and optical elements (a scanning lens and a mirror) for imaging the scanning light beam deflected by the polygon mirror on a surface of a photoconductor, and a photosensor is provided outside an effective light exposure area at the side of starting scan in order to determine a writing start position.
In such a color image forming apparatus, it is necessary to superpose plural colors when a color image is formed. There are provided a method for superposing images with plural colors on one photoconductor and a method for superposing images with plural colors on plural photoconductors.
However, tilt of a scanning line in main-scanning directions or a resist deviation in sub-scanning directions may be caused depending on, for example, the field curvature characteristic of an optical element, twisting of an optical housing, thermal deformation caused by heat generation of a polygon motor, thermal deformation caused by a heat source that is another unit in a body, and twisting at the time of attaching a photoconductor, and thereby a color shift is caused in a color image forming apparatus since three or four scanning lines are not superposed.
Main scanning directions are directions in which writing is conducted on a recording medium by an optical scanning device itself, and sub-scanning directions are directions in which a transcription medium is moved, wherein the sub-scanning directions are directions that are generally orthogonal to the main-scanning directions.
The tilt of a scanning line toward sub-scanning directions is a phenomenon such that it is tilted toward the sub-scanning direction with respect to an ideal scanning line. The resist deviation in sub-scanning directions is a phenomenon such that parallel shift is caused to the sub-scanning direction with respect to an ideal scanning line.
Particularly, when both ends of a mirror are fixed by leaf springs, the arrangement of the mirror is fixed and it is difficult to adjust the mirror.
In order to solve this problem, conventional techniques, for example, in Japanese Patent Application Publication No. 2001-100135, are proposed. According to this, one end portion of a mirror in the longitudinal directions thereof is attached to an adjustment mechanism and the other side of the mirror is attached to a mirror support with a holding mechanism. The adjustment mechanism side thereof is supported by an elastic member such as a leaf spring and setting screws for the two-point support thereof while the mirror is clipped. Also, the holding mechanism side thereof is pressed by a mirror fixing member such as a leaf spring onto the supporting point of mirror rotation which is provided in an optical housing so that it is rotatably supported.
As the two setting screws described above are rotated by the same angle, the two setting screws are moved forward or backward by the same extent whereby the mirror is shifted to the sub-scanning direction and the tilt of a scanning line can be controlled. On the other hand, as the two screws are rotated by angles different from each other, the mirror is rotated centered on the supporting point of rotation and the deviation of the scanning positions can be controlled whereby a high-quality color image with a little color shift can be output.
In the above-mentioned conventional technique, although the tilt of a scanning line toward the sub-scanning directions and the resist deviation in the sub-scanning directions can be changed, the adjustment mechanism is complex and the number of components is increased thereby causing a cost increase. An adjustment member such as a setting screw cannot control the positional deviation with a high precision since the resolution in regard to the adjustment precision is low. Also, since the angular rotation of the two setting screws are conducted, it takes a long time to conduct adjustment thereby causing an increase of manpower.
In regard to an optical scanning device, cost reduction by means of simplification of each component, reduction of the number of components, or reduction of a time period required for assembly and adjustment is desired in order to attain a low price of a digital copying machine or a laser printer.
In addition, when both ends of a mirror are fixed by an adhesive material, a mirror and a mirror holding member of an optical scanning device which holds a mirror is thermally expanded or shrunk with a temperature change of the optical scanning device. In general, since the coefficient of linear expansion of a mirror is different from the coefficient of linear expansion of a mirror holding member of an optical scanning device which holds a mirror, the mirror is curved depending on the temperature change of the optical scanning device when both ends of the mirror is rigidly fixed by an adhesive material, and accordingly, the performance of the optical scanning device using a mirror may be degraded. Therefore, for an adhesive material for bonging both ends of a mirror, it is necessary to use a relatively soft adhesive material which can allow for the thermal expansion or shrinkage of a mirror but it may be difficult to bond a mirror rigidly.
In such a situation, the inventors have found that it is possible to provide an optical scanning device which is capable of adjusting arrangement of a mirror and in which a mirror distortion caused by heat is reduced, an image forming apparatus which comprises the optical scanning device, a mirror which is capable of being bonded rigidly and more easily, a housing which is capable of bonding a mirror thereto rigidly, a mirror attaching method which is capable of adjusting arrangement of a mirror and in which a mirror distortion caused by heat is reduced, a mirror arrangement adjusting device which is capable of adjusting arrangement of a mirror more easily, and a mirror arrangement adjusting method which is capable of adjusting arrangement of a mirror more easily.